[pve-devel] Custom storage plugins API

[Alexander Schmid]

Hello Dietmar,
has someone found time to have a look at this ?

For finishing my SCST-Plugin it would be good to know if there will be a 
way to catch qemu-img convert from a custom implementation.
Also, as my plugin activates snaps temporary via a clone of the snap and 
exposes this as an iscsi-target, it would be crucial that 
deactivate_volume is called for cleanup.

Really would love a way to clone from older Snapshots with ZFS over 
iSCSI but don't feel very comfortable with the situation that the 
storage-plugin needs patching other parts like QemuServer.pm

Worst-case, i`d think about bundling the plugin in a .deb with 
dependencys and post-install triggers that do the patch to prevent 
breaking the storage with an PVE-Update. But this is really not what i 
want to do ...


Guess some of the things how it allows to access older snapshots in ZFS 
might also be a nice addition to the zfsplugin in general.
I think it should work with the bundled iscsi-targets, too.

Best regards,
Alex


Am 13.01.17 um 10:55 schrieb Alexander Schmid:
> Am 13.01.17 um 10:44 schrieb Dietmar Maurer:
>>> I also extended ZFSPlugin to allow access to Snapshots (via zfs 
>>> snapshot
>>> + clone + iSCISI Target on the Clone) and cloning from Snapshots (via
>>> send/rcv on a clone). Therefore i had some minor changes in
>>> QemuServer.pm to allow this. Any chance these could be taken into 
>>> one of
>>> the next releases ?
>> A first step would be to send the code to list (else nobody known what
>> you really talk about).
>>
> Currently, i only changed qemu_img_convert to allow sort of delegation 
> to the storage-plugin. See comments.
>
> This would let the storage-plugin jump-in, in my case zfs send/rcv is 
> used in favour of qemu-img convert as it's much faster.
>
> Not sure about the call of deactivate_volume in the end and if it 
> might break other storage implementations.
>
> I needed it to do some cleanup on the iscsi-targets that were 
> temporary created on the snap.
>
> sub qemu_img_convert {
>     my ($src_volid, $dst_volid, $size, $snapname, 
> $is_zero_initialized) = @_;
>
>     my $storecfg = PVE::Storage::config();
>     my ($src_storeid, $src_volname) = 
> PVE::Storage::parse_volume_id($src_volid, 1);
>     my ($dst_storeid, $dst_volname) = 
> PVE::Storage::parse_volume_id($dst_volid, 1);
>
>     if ($src_storeid && $dst_storeid) {
>
>     PVE::Storage::activate_volumes($storecfg, [$src_volid], $snapname);
>
>     my $src_scfg = PVE::Storage::storage_config($storecfg, $src_storeid);
>     my $dst_scfg = PVE::Storage::storage_config($storecfg, $dst_storeid);
>
>     my $src_format = qemu_img_format($src_scfg, $src_volname);
>     my $dst_format = qemu_img_format($dst_scfg, $dst_volname);
>
>     my $src_path = PVE::Storage::path($storecfg, $src_volid, $snapname);
>     my $dst_path = PVE::Storage::path($storecfg, $dst_volid);
>
>     #BEGIN addition
>     my $src_storage_plugin = 
> PVE::Storage::Plugin->lookup($src_scfg->{type});
>     my $dst_storage_plugin = 
> PVE::Storage::Plugin->lookup($dst_scfg->{type});
>
>     # in many cases the storage may have a better idea how to convert:
>     # if src and dst format is the same
>     # and src_storeid is dst_storeid
>     # and the storage has the feature
>     # and the feature is implemented as volume_copy / 
> volume_snapshot_copy
>     # let the storage do the work as it quite sure is faster
>     if ( $src_format eq $dst_format ) {
>         if( $src_storeid eq $dst_storeid ) {
>             # this is the same storage
>             # and storage is capable of materializing snaps
>             if( $snapname ) {
>                 my $canCopySnap = 
> PVE::Storage::volume_has_feature($storecfg, 'copy', $src_volid, 
> $snapname, undef) && $src_storage_plugin->can('volume_snapshot_copy');
>                 if( $canCopySnap ) {
>                     print "delegate to storage plugin 
> volume_snapshot_copy (snap $snapname)\n";
> $src_storage_plugin->volume_snapshot_copy($src_scfg, $src_volname, 
> $snapname, $dst_volname);
>
> $src_storage_plugin->deactivate_volume($src_storeid, $src_scfg, 
> $src_volname, $snapname);
>
>                     return 1;
>                 }
>             }
>
>             my $canCopyVolume = 
> PVE::Storage::volume_has_feature($storecfg, 'copy', $src_volid, undef, 
> undef) && $src_storage_plugin->can('volume_copy');
>             if ( $canCopyVolume ) {
>                 print "delegate to storage plugin: volume_copy (base)\n";
>                 $src_storage_plugin->volume_copy($src_scfg, 
> $src_volname, $dst_volname);
>
> $src_storage_plugin->deactivate_volume($src_storeid, $src_scfg, 
> $src_volname, $snapname);
>
>                 return 1;
>             }
>         }
>     }
>     #END addition
>
>
>     my $cmd = [];
>     push @$cmd, '/usr/bin/qemu-img', 'convert', '-p', '-n';
>     push @$cmd, '-s', $snapname if($snapname && $src_format eq "qcow2");
>     push @$cmd, '-f', $src_format, '-O', $dst_format, $src_path;
>     if ($is_zero_initialized) {
>         push @$cmd, "zeroinit:$dst_path";
>     } else {
>         push @$cmd, $dst_path;
>     }
>
>     my $parser = sub {
>         my $line = shift;
>         if($line =~ m/\((\S+)\/100\%\)/){
>         my $percent = $1;
>         my $transferred = int($size * $percent / 100);
>         my $remaining = $size - $transferred;
>
>         print "transferred: $transferred bytes remaining: $remaining 
> bytes total: $size bytes progression: $percent %\n";
>         }
>
>     };
>
>     eval  { run_command($cmd, timeout => undef, outfunc => $parser); };
>     my $err = $@;
>
>     # added: deactivate the src-volume, even on failure
>     # this can be safely called as qemu_img_convert is never called on 
> a running volume (that is not a snap)
>     $src_storage_plugin->deactivate_volume($src_storeid, $src_scfg, 
> $src_volname, $snapname);
>
>     die "copy failed: $err" if $err;
>
>     }
> }
>
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